It is known from practice, and for instance from EP 0 667 415 A1, that certain automotive building machines, e.g., road finishers or chargers, have to be supplied with material during their operation. This process, which is called charging, is carried out during the driving operation, for instance by a truck driving backwards and approaching the road finisher or charger, which moves forwards at the same time, and tipping the material from its load area into the material hopper of the road finisher or charger. While the charging takes place the truck is pushed forward by the road finisher or charger.
It is furthermore known that, for charging purposes, the truck docks to a push-bar of the road finisher or charger so as to position its load platform above the material hopper such that no material gets lost during the unloading. To prevent the road finisher or charger from being abruptly dislocated backwards on the ground during the docking of the truck, respectively, while the truck is pushed forward the push-bar is conventionally mounted in a resilient, respectively, damping fashion.
A road finisher having a docking unit is disclosed, for example, in DE 10 2011 120 161 A1. Seen in the driving direction, the docking unit is provided in the front, underneath the material hopper. The docking unit comprises a push-bar which is resiliently mounted by means of elastomeric profile dampers. The drawback thereof is the fact that the elastomeric profile dampers become hard and brittle in the course of time so that in particular the damping characteristic of the docking unit changes in an undesirable manner.
Documents U.S. Pat. No. 5,004,394 A and EP 2 295 641 A2 each disclose a road finisher comprising a docking unit. The push-bar of the docking unit is supported by two controllable hydraulic cylinders. The respective hydraulic cylinders are coupled, on opposite sides of the piston, to a hydraulic system provided in the road finisher. The respective pistons of the hydraulic cylinders can thus be shifted between a moved in and a moved out position by externally introducing a hydraulic fluid into the hydraulic cylinders. The disadvantage thereof is the fact that the connection of the respective hydraulic cylinders to the hydraulic system of the road finisher is cost-intensive, and the hydraulic lines connected to the hydraulic cylinders require plenty of space on the road finisher.
Moreover, additional electronic components are required on the road finisher for controlling the hydraulic system, viz. positioning the respective hydraulic cylinders as desired, thus increasing the production costs.
A bumper for motor vehicles is disclosed in DE 2 243 076 A. The bumper includes a first and second damper connected to each other crosswise by means of hydraulic lines, allowing hydraulic fluid to be displaced from a piston rod side of the first damper into the piston side of the second damper, and hydraulic fluid to be displaced from the piston side of the first damper into the piston rod side of the second damper. The respective dampers further comprise a dividing piston delimiting a gas space in the damper and serving to compensate a volume change. The respective dampers are further connected to a regeneration system externally supplying a hydraulic fluid to the dampers so as to move the dampers back into an initial position after an impact. The disadvantage thereof is the fact that connecting the dampers to one another, and coupling the respective dampers to the hydraulic regeneration system, requires plenty of space in the motor vehicle. At the same time, there is a great need for maintenance and servicing.
EP 2 527 534 A1 discloses a road finisher comprising a push-bar which is carried by a damper. The damper includes a friction spring the damping rate of which during the spring compression differs from that during the spring release.